Residual Stress Behavior of DLC Film

in Humid Environment

Young-Jin Lee a),b), Tae-Young Kim a),Kwang-Ryeol Lee a), In-Sang Yang b)

a) Future Technology Research Division, KISTb) Department Of Physics, Ewha Womans Univ.

Introduction

Low friction and high wear resist

Chemical inertness

Various application

Artificial Knee Joint

Artificial Hip Joint

High hardness

VCR head drum

Hard disk

Disadvantage

T. Ohana at al. Diamond Rel. Mater., 13 (2004) 1500

Environment dependence of DLC film.

Tribo test under aqueous condition

Tribo test under dry condition

S. J. Park at al. Diamond Rel. Mater., 12 (2003) 1517

Two Possibilities of Film Delamination

Residual stress is changed by water molecules.

Interfacial energy is changed

by water environment.

Film delamination enhanced.

Possibility 2.

Film delamination enhanced.

Possibility 1.

Purpose of This Work

• To investigate the residual stress behavior of various DLC films in humid environment systematically.

• To find the reason for the humidity dependence of DLC film in the point of residual stress.

Stress Measurement

• In Situ stress measurement : kMOS (Multi-beam Optical Sensing). (k-space Associate, Inc.)

• Humidity control : 10 ~ 90 % in air (± 5%). step control.

• Temperature : room temperature(19~26°C).

• Measurement time : about 600sec for each step.

• Stress measurement resolution : maximum 4Km in radius (In this system 1MPa)

Synthesis of DLC Films

• r.f. PACVD (13.56 MHz)

• Precursor Gas : C6H6, CH4

• Deposition Pressure : 1.33 Pa

• Bias Voltage : -100V ~ -800V

• Substrate :

P-type (100) Si-wafer 525 ㎛

P-type (100) Si-wafer 200 ㎛ (5×50

㎜ )

• Film Thickness : 500 ㎚

Residual Stress & Film Structure

1000 1250 1500 1750 20000

5000

10000

15000

20000

25000

Benzene -100V

Methane -150V

Methane -500V

Inte

nsity

(a.

u.)

Wave Number (cm-1)

0 -200 -400 -600 -8000.0

0.5

1.0

1.5

2.0

S

tres

s(G

Pa)

Bias Voltage (V)

0 -200 -400 -600 -800

1.0

1.5

2.0

2.5

3.0

3.5

Str

ess(

GP

a)

Bias Voltage (V)

C6H6 CH4

C6H6 -100V

Polymeric film

CH4 –500V

Graphitic film

CH4 –150V

Diamond-like film

Polymeric FilmPolymeric Film in Humid Condition

-10

0

10

20

30

Elapsed Time

(

MP

a)

20%50%90%80%50%20%

R.H. 20%→ 90%

16MPa↑

Immediate & reversible stress response

Compressive residual stress ∝ Relative humidity

-10

0

10

20

30

(

MP

a)

Elapsed Time

75% 20%90%55%

20%

Diamond-like FilmDiamond-like Filmin Humid Condition

R.H. 20%→ 90%

No change

Compressive residual stress has no relationship with humidity.

-10

0

10

20

30

(

MP

a)

Elapsed Time

25%90%40%20%

Graphitic FilmGraphitic Filmin Humid Condition

R.H. 20%→ 90%

12MPa↑

Immediate & reversible stress response

Compressive residual stress ∝ Relative humidity

Summary Ⅰ

• Residual Stress of DLC film has a humidity dependence.

• This is related with the film structure.

• Especially in polymeric and graphitic film, the compressive residual stress increase as humidity increases.

• Diamond-like film is no relationship with humid condition.

Effect of Water Molecule

F1 F1

>

F2

=

substrate substrate

substrate substrate

F1

Case 1.Reaction at surface

Case 2.Water penetration

Thickness Effectin Humid Condition

20 40 60 80 100

0

10

20

30

(

MP

a)

Relative Humidity (%)

400nm 500nm 1000nm

Polymeric DLC film

R.H. 20%→ 90%

400nm film : 27 MPa↑500nm film : 16 MPa↑1000nm film : 9 MPa↑

400 600 800 1000

0

10

20

30

(

MP

a)Thickness (nm)

Effect of Water Molecule

F1 F1

>

F2

=

substrate substrate

substrate substrate

F1

Case 1.Reaction at surface

Case 2.Water penetration

Effect of Water Molecule

F1 F1

>

substrate substrate

Case 1.Reaction at surface

s o f so

f f

F t F

t t

0

sF

ft

: Initial residual stress

: added force

: film thickness

In the case of polymeric DLC film, added surface force is

9.4±1.4 Nm-1

Conclusion

• Residual stress of DLC film has a relationship with humid condition. It is related with the film structure. Especially in polymeric and graphitic DLC film, compressive residual stress increase as the humidity increases.

• It is possible to enhance the stability of DLC films by structure control.

• This is due to the reaction between water molecules and film surface.

• During residual stress is changed, the structure or chemical composition is not changed.

• Humidity dependence of residual stress could be controled by surface treatment.